[Icom] Wider SSB bandwidth on IC-756

[Bill Gode, Sr.]

Gene,

Yes, the switch is present on later versions, but changing it from N to
W seems to increase the chances for unwanted distortion, in addition to
widening the transmit signal by about 200 Hz.  I measured additional
response in both lows and highs of about 100 Hz at either end, but
returned my switch to N after testing.  

This is a TRANSMIT mod and has nothing to do with the receive filters
(stock or optional).  My guess is that the switch bypasses the 2.8 kHz
filter, which is probably used as a roofing filter for the transmit
DSP.  This switch appeared after the major IC-756 mods came out at about
s/n 1900 to clean up the transmitter.  It is not mentioned in the
Service Manual and Icom-America was unable to provide any information.
(Surprise!) 

See: <http://www.mods.dk/select.php3?id=2326&radio=Icom&model=IC-756>

If you want really wide SSB receive response, plug an FL-102 9 MHz "AM
Filter" in the optional 9 MHz filter slot and "fool" the IC-756 into
thinking it has the narrow ssb filter installed.  If you configure the
filter menu properly, you can run FL-102 along with the 9 kHz filter at
455 kHz IF in the ssb "narrow" mode and recover audio out to beyond 4
kHz before the DSP rolls off the response.  

The FL-257 will get you from 2.8 kHz out to 3.3 kHz wide - RECEIVE ONLY.

73,

Bill, W9NHQ

"Gene A. Williamson" wrote:
> 
>         In a review comparing IC-756 and 756Pro/II, W8WWV states the following:
> 
> NOTE: In January of 2002, I learned that some amateurs had discovered that
> models of the 756 past a certain serial number were built with a
> normal/wide transmit audio bandwidth switch. The serial number of the
> change appears to be around 3,000. The switch is totally undocumented, and
> is located within the radio. The switch, S801, is on the bottom of the
> radio. I do not know where it is located. The swiched is marked N (normal)
> and W (wide). By default, it should be in the N position. If you move the
> switch to the other position, your transmit audio bandwidth will become wider.
> 
>         Can anyone here confirm that? And comment on how the "Wide" setting would
> compare to using ICOM's FL-257 3.3kHz filter? I don't work SSB, but
> thinking about doing so, and am intrigued with the "Hi-Fi SSB" concept.
> 
> 73 Gene N7YW
>